The light-emitting diode (LED) converts a forward current into light. In a forward-biased PN junction of the LED, minority carriers are injected across the junction and diffused into the P and N regions. The diffused minority carriers then recombine with the majority carriers. Such recombination gives rise to light emission.
LEDs are very popular elements. They can function as a light source for producing light in a variety colors and wavelengths. In an LED-lighting system, a light source includes a red LED, a green LED, and a blue LED, and a variety of colors can be produced by changing intensities of these LEDs. Conventionally, controlling the illuminations or colors of the light source is usually achieved through an operation interface, such as a button or a knob. Today, an infrared transmitting-and-receiving device is implemented in the lighting system for controlling the light source to output light with a specific illumination or color.
FIG. 1 is a diagram showing a conventional lighting system disclosed in a patent No. W2006/056814, where the lighting system adopts the infrared transmitting-and-receiving device for controlling the light source. As indicated, the lighting system 50 includes an infrared transmitting-and-receiving device 60 and a light unit 61. When an object 70, say, user's hand, enters a detectable zone of the infrared transmitting-and-receiving device 60, an infrared-wave 62, emitted from the infrared transmitting-and-receiving device 60, will be reflected by the object 70, and the reflected infrared-wave 63 is then received by a receiver 71 within the infrared transmitting-and-receiving device 60. According to the magnitude of the reflected infrared-wave 63 and the distance between the object 70 and the infrared transmitting-and-receiving device 60, the changes of the position of the object 70 related to the infrared transmitting-and-receiving device 60 is obtained. The lighting system 50 can control the light unit 61 to output light with a specific illumination or light color according to the changes of the position of the object 70.
However, adopting the infrared transmitting-and-receiving device 60 in the lighting system 50 results in some obvious defects. For example, the accuracy of the infrared transmitting-and-receiving device 60 is easily affected by the illumination around the infrared transmitting-and-receiving device 60. Moreover, the operation range of the infrared transmitting-and-receiving device 60 is limited to about 30 cm due to the magnitude decreasing of the reflected infrared-wave 63.
Instead of the infrared transmitting-and-receiving device, the ultrasonic transmitting-and-receiving device can be implemented in the lighting system. Using the ultrasonic transmitting-and-receiving device for determining the distance between an object and the ultrasonic transmitting-and-receiving device is a well-known technique. When an object enters a detectable zone of the ultrasonic transmitting-and-receiving device, an ultrasonic-wave, emitted from the ultrasonic transmitting-and-receiving device, will be reflected by the object, and the reflected ultrasonic-wave, called echo signal, is then received by the ultrasonic transmitting-and-receiving device. The period between the ultrasonic transmitting-and-receiving device emitting the ultrasonic-wave and the ultrasonic transmitting-and-receiving device receiving the echo signal is defined as TOF (time of flight). Obviously, the value of TOF is proportional to the distance between the object and the ultrasonic transmitting-and-receiving device.
FIG. 2 is a diagram showing the lighting system having an ultrasonic transmitting-and-receiving device for controlling the light source. As shown in FIG. 2, the lighting system includes: a light source 11 and an ultrasonic transmitting-and-receiving device 12. The light source 11 is LEDs, and further includes of a red LED (R), a green LED (G), and a blue LED (B). When an object 13 enters a detectable zone of the ultrasonic transmitting-and-receiving device 12, an ultrasonic-wave, emitted from the ultrasonic transmitting-and-receiving device 13, will be reflected by the object 13. The echo signal is then received by the ultrasonic transmitting-and-receiving device 12. According to the value of TOF, a microprocessor in the lighting system (not shown in FIG. 2) can determine the distance R between the object 13 and the ultrasonic transmitting-and-receiving device 12. The lighting system then generates a control signal according to the distance R for controlling the light source 11 to output light with specific light properties (such as color or light illumination). For example, the light source 11 of the lighting system can be designed to output light with a first color if the distance R between the object 13 and the ultrasonic transmitting-and-receiving device 12 is determined to be R1; the light source 11 outputs light with a second color if the distance R is R2; the light source 11 outputs light with a third color if the distance R is R3 and so on. Or, the light source 11 outputs light with a first illumination if the distance R is R1, a second illumination if the distance R is R2, a third illumination if the distance R is R3 and so on.
However, the above-mentioned lighting system cannot control more than one light property through the change of the distance R. In other words, the lighting system is only capable of changing either the light color or the light illumination. Moreover, due to the limit of the distance R between the object 13 and the ultrasonic transmitting-and-receiving device 12, the number of light with different light properties is accordingly limited.